Not Applicable
Not Applicable
This invention relates to a die for a rotary compression press. As is known, rotary compression presses have top and bottom rams which are axially guided in respective die guides of the rotor and which interact with die-plate bores of the die-plate. Actuation of the rams is effected by means of stationary control cams. The compressing process, which is performed by means of the rams, is caused by pressure rollers against which the rams run and which press the rams downwards or upwards for the purpose of compressing the powdered material filled into the die-plate bores.
It is known to shape the rams from two portions, namely a shank-like holder which interacts with the pressure rollers and an insert which is adapted to be releasably connected to the ram holder. The ram insert constitutes the compressing process tool proper and, thus, determines the contour of the compact.
From the utility model DE 88 16 064, a rotary compression press has become known in which the shank of the compressing rams has a toothing which interacts with a toothed rack which is stationary. The rotary motion of the top and bottom rams immediately following the compressing process and during the extraction of the rams from the die-plate bore is intended to achieve a separation from the surface of the compacted tablet.
From EP 0 448 190, a rotary compression press has become known in which the top and bottom rams are guided in bushings which, in turn, are rotatably supported and toothed in order to cooperate with a stationary toothing. The ram shanks are linearly guided in the bushings. For a reduction in wear on the pressure rollers and those heads out of the heads which face the rollers it has also become known to design the rams in two portions and to configure them so as to be rotatable against each other. The gear-operated drive now takes place only on the lower ram portion which as was stated can be rotated with respect to the upper one.
It is the object of the invention to provide a die for rotary compression presses in which a separate drive may be dispensed with for a relative rotation with respect to the compacted tablet.
According to the invention, the projection of the die insert is helically guided in the bore between axially spaced stops and is biased by a spring towards the front-end face of the die holder. At the start of a compressing process, the die insert moves into the die holder up to a firm stop. During this axial motion, a limited rotary motion of the die insert takes place at the same time. After the compressing operation, the die is raised and the spring restores the die insert back to the initial position. At this time, the die insert performs a rotation, which causes it to separate from the tablet.
Various constructional solutions can be imagined in realizing a die of the type described. According to an aspect of the invention, one consists in that a threaded spindle is connected, in a non-rotary relationship, to the free end of the projection and the bore has disposed therein, in a non-rotary relationship, a spindle nut with which the threaded spindle interacts. According to another aspect of the invention, the spindle nut may be located by means of radial pins in the die holder. According to a further aspect of the invention, the projection of the die insert has at least one radial trunnion which engages a groove of the die holder wherein said groove is sized so as to allow for an axial motion of the die insert. According to a further aspect of the invention, the trunnion can be the end of a radial pin by which the spindle is located in a bore of the projection. For an efficient transmission of the compressing force from the die holder onto the die insert, an aspect of the invention provides that the axial motion of the die insert is limited by its abutting action against the front-end face of the die holder.
For an efficient separation of the die face from the surface of the compacted tablet, it is sufficient to effect a relative rotational motion through a limited angle of rotation. For example, the angle of rotation is 10 to 30xc2x0, preferably about 20xc2x0.
The invention will now be explained in greater detail with reference to an embodiment shown in a drawing.